' Л1ГЛ-Г—""'1 -V Apr]"ratinr of FP''S 'v|p'"tror ppprirnprnp- for rhpmdoal Rnp];Fi?) i o radialior ^ViPmisir' and Tri oi or: csl molficules - •] We regret that copy of this r legibility sta copy was used Df Scientific Вас Already i electron speci ;. i-i; FINAL REPORT to study the 1 1 •'. •' ^ systems. The 1 shifts of the method was gi1 - I Contract number; 971/RB. Chemical Anal; ¡I the shifts in Title of project; atoms. A numb Application of E3CA (Electron Spectroscopy for Chemical betv/een chemi Analysis) to radiation chemistry and biological molecules. higher extent !:S to all elemen Research Institute; light first a Institute of Physics, Uppsala University, Uppsala, Sweden. especially in applied to s Chief scientific investigator; hemoglobine Professor Kai Siegbahn valuable inf( active sites Period of contract: development I97I-OI-OI—I973-I2-3I • investigatioi a few system ment in expe limit of exi A major 'i'--'. -• taken in 197 generation Б earlier not chromatizat: ^ fine focuss Scientific Background and Scope of Fro.ject geometrical Already in the early stages of the development of positron se electron spectroscopy it became clear that it is possible project was to study the electronic structure of atoms in molecular the aim of systems. The molecular influence is observed as chemical chemistry a shifts of the atomic core electron levels, whereof the method was given the name ESCA (Electron Spectroscopy for Experimenta Chemical Analysis). Moreover, it v/as possible to interpret The ex the shifts in terms of effective charges on the observed follows: atoms. A number of useful correlations have been established The sa between chemical shifts and atomic charges. ESCA is to a chromatized higher extent than most other spectroscopic methods applicable electrons a to all elements of the periodic oystem, in particular to the given by light first and second row elements. This makes ESCA interesting especially in organic chemistry, and at an early stage it was applied to some large biological molecules such as insuline, where hv is hemoglobine aiid cytochrome C. ESCA turned out to give electron ii valuable information of the valence state and reactivity at the function C( active sites in these systems. At that time the experimental high power development was by far not yet completed and these preliminary emission ti investigations could be made only with considerable efforts for (8000 rpm) a few systems. However, it was clear that a substantial improve- the emitte< ment in experimental performance could be reached within the analyzer, limit of existing technology. plane onto are í'irst A major step in the necessary instrumental development was towards a taken in 1970 when the design of the prototype of the new registered generation ESCA instruments started. It comprises several system. earlier not exploited technical improvements, such as mono- chromatization of the X-rays, a high power X-ray tube with a Durin fine focussing electron gun and a rotating anode, an improved geometrical arrangement in the source compartment and a new positron sensitive multidetector system. The scope of this project was to further develop the experimental technique with the aim of making E3CA a more general method also in bio- chemistry and radiation chemistry. Experimental methods The experimental technique can shortly be described as follows: The sample to be studied is irradiated by a beam oi' mono- chromatized soft X-ray photons. By the photoelectric process electrons are emitted with a characteristic energy, E, . given by where hv is the photon energy, B_ is the binding energy of the electron in the isth level and í is a spectrometer work function constant. The monochromatic X-rays are created in a high power X-ray tube consisting of a fine focussing high emission two stage electron gun (15 kV/400 mA) and a high speed (8000 rpm) water cooled rotating anode. The kinetic energy of the emitted electrons is measured by a spherical electrostatic analyzer. After 180 the electrons are focussed in a focal plane onto a position sensitive electron detector. The electrons are first multiplied by a factor of 10 and then accelerated towaras a phosphor screen. The resulting light pulses are registered by a vidicon tube connected on-line to a computer system. During the course of this project also the first steps were taken to extend the ESCA technique to molecular and liquids. The possibility of making ESCA studie3 of liquid systems have met particularly strong interest among organic chemists. A new sample handling system was developed by which the liquid was introduced as a well collimated beam in the sample compartment. This also demanded that effective differential pumping was introduced. Results The new prototype instrument was brought into operation at the end of 1972. The expected improvement in resolution was achieved. The width of the exciting AlKa- radiation was reduced from 0.8 eV to 0.2 eV. In addition, the X-ray satellites and the continuum bremsstrahlung were effectively eliminated. Hereby the signal-to-background ratio was considerably improved. Compared to previous instruments the total intensity was increased by a factor of 100. In particular, the new much higher sensitivity made possible the study of large molecules in the gas phase. A vapour pressure of > 10 torr at a temperature of < 150° С is sufficient and hence a majority of common organic compounds are available for the study in the gas phase. As an example we may mention the study of the charge-transfer complex pyridine-iodomono- chloride where ESCA as the first spectroscopic method could establish the amount of transferred charge in the bond. This is particularly interesting since charge-transfer type of bonding is frequently found in biological systems. The first spectra from liquids in E3CA were recently recorded. Especially interesting is that now compounds in Papers Publ: solutions and chemical reactions such as the formation of complexes can be studied. The technique is still under development and a number of improved "liquid cells" are presently being tested. 2. Electron Siegbahn "Encyclo; Conclusions McGraw-H; The results on the prototype instrument showed that this was the correct line to proceed. Therefore, last year we started to develop the completed version of the new generation of ESCA instruments. The design philosophy 4» Perspect Siegbahn has been to extend the performance of each component to a "Electro. Publ. Co practical limit, mainly set by physical reasons. The 5. Molécula intensity can hereby be enhanced by an additional factor Gelius, : 2 "Electro of 10 and the resolving power can be further improved. Publ. Co Two instruments of this kind are under construction. The first one is planned to be brought into operation by the end of this year. With this instrument the aira of this 7. Chemica: project will be reached of developing ESCA as a method for Gelius, Allison work also on biological molecules. J. Elec 8. Electroi Siegbahi "Atomic Plenum 9. ESCA st gas pha Gelius, Faraday 10. Theory Gelius, UÜIP-81 11. ESCA aj and lee Khodey< Chem. Papers Published on Work under the Contract. 1. The ESCA spectra of benzene and the iso-electronic series, thiophene, pyrrole,and furan. Gelius, U., Allan, C.J., Johansson, G., Siegbahn, H., Allison, b.A. and Siegbahn, K. Physica Scripta ¿, 237 (1971). 2. Electron spectroscopy. Siegbahn, K. "Encyclopedia of Science and Technology" p. 585. McGraw-Hill Third Edition 1971* 3. The electronic structure of carbon suboxide from ESCA and ab initio calculations. Gelius, U., Allan, C.J., Allison, D.A. Siegbahn, H. and Siegbahn, K. Chera. Phys. Lett. J_l» 224 (1971). 4. Perspectives and problems in electron spectroscopy. Siegbahn, K. "Electron Spectroscopy". Ed. D.A. Shirley, North-Holland Publ. Co., Amsterdam 1972, p. 15» 5. Molecular orbitals and line intensities in SSCA spectra. Gelius, Ü. "Electron Spectroscopy". Ed. D.A. Shirley. North-Holland Publ. Co., Amsterdam 1972, p. 311» 6. Molecular spectroscopy by means of ESCA. V. Boron compounds. Allison, D.A., Johansson, G., Allan, C.J. Gelius, U., Siegbahn, П., Allioon, J. and Siegbahn, K. J. Electron Spectrosc. J_, 269 (1972/73). 7. Chemical shifts in ESCA and ffiffi. Gelius, П., Johansson, G., Siegbahn, H., Allan, C.J., Allison, D.A., Allison, J. and Siegbahn, K. J. Electron Spectrosc. J_, 285 (1972/73). 8. Electron spectroscopy for chemical analysis. Siegbahn, 1С. "Atomic Physics", Vol. 3. Ed. S.J. Smith and G.K. Walters. Plenum Publ. Co., New York 1972, p. 493. 9. ESCA studies of molecular core and valence levels in the gas phase. Gelius, U. and áiegbahn, K. Faraday Discussions of the Chemical Society _54_, 257 (1972). 10. Theory of binding energies and chemical shifts in ESCA. Gelius, U. ÜÜIP-819 (March 1973). 11. ESCA applied to high temperature molecular beams of bismuth and lead. Khodeyev, Y.S., Siegbahn, H., Hamrin, K. and Siegbahn K. Chem. Phys. Lett. ЛЭ., 16 (1973). 12. A high resolution E5CA instrument with X-ray monochromator for gases and solids. Gelius, U., Basilier, E., Gvensson, S., Bergmark, T. and Siegbahn, K. UUIP-817 (April 1973). 15» Design principles in electron speetroscopy, V/annberg, В., Gelius, Ü. and Siegbahn, K. ÜUIP-918 (April 1973)* 14. Molecular spectroscopy by means of ESCA. Gelius, Ü. Acta Univsrsitatis Upsaliensis 242 (197?)« (Thesis) 15» Electron spectroscopy - a new way of looking into matter. Siegbahn, K. Endeavour ¿2, 51 (1975). 16. ESCA applied to liquids. Siegbahn, H. and Siegbahn, K. J. Electron Spectrosc. ¿ (1975)- 17* Pyridine-iodoroonochloride. A charge transfer complex studied by ESCA. Kostad, Asbj., Svensson, S., Hilsson, R», Basilier, E., Gelius, U., Nordling, C. and Siegbabn, K. Chem. Phys. Lett. 23, 157 (1973)..